The present invention relates to a process for treating particulate matter, in which particles of the material to be treated interact with a non-static second set of particles. The present invention also relates to a reactor apparatus for performing the said process.
A number of techniques have been developed for processing of refractory ores or chemically bonded substrates and these fall into two main categories: hydrometallurgical techniques, such as pressure oxidation and biological leaching; and pyrometallurgical techniques, such as roasting, pyrolysis and calcination.
Several metals occur naturally as the sulphide, for example galena (PbS), copper pyrites and chalcopyrite (Cu2S with FeS), pentlandite (NiS with Cu2S and FeS), and zinc blende and sphalerite (ZnS). The metal is extracted from the ore by a reducing or electrowinning process, but it is common to first convert the sulphide into an oxide in a preliminary roasting process. In such a process, the sulphide ore is powdered and then roasted to the oxide by heating in air at a temperature below the melting point of either the sulphide or oxide. Roasting reactions are often exothermic and the heat released provides much or all of that needed to keep up the temperature during the roast. During roasting, the particles of powder may become stuck together, i.e. sintered, so forming agglomerates. If sintering develops too quickly, then oxygen may fail to reach all of the particles and some sulphide will remain and in extremis a fluidisation process will fail as particles grow excessively. A process of flash roasting in a dilute spouting bed reactor is known in the art (Australian Engineering and Mining Journalxe2x80x94June 1993 pp 23). In a flash roaster, hot gases enter a vertical reactor assembly through a narrow throat or venturi which provides a region of high gas velocity. Feed solids are then introduced into the gas stream directly above the venturi, which due to the high gas velocity in the throat prevents weeping of the solids. For large particles the reactor behaves as a back-mixed reactor, whilst fine particles are elutriated directly, and hence the behaviour is more plug flow, that is there is essentially little or no mixing or diffusion of the particles along the flow path.
There are a number of disadvantages associated with systems based on the dilute spouting bed technique. Thermal profiles can be generated across the reactor and between the gas phase spout and the surrounding dense bed leading to poor temperature control resulting in unprocessed material and/or agglomeration or possible sealing over the outer surfaces of the reactant particles reducing access to the particle interior. It is also often difficult to control the temperature in the event of an exotherm. Furthermore, as a result of the bi-modal characteristics of the technique, there is a wide distribution of particle residence times. The residence time is furthermore strongly dependent on the material to be treated. This system is also unable to cater for very finely divided feed stocks, or feed stocks with large exotherms.
Further the use of fluidised beds is common whereby the mineral concentrate is introduced, often as a wet filter cake, directly into the fluidised bed with similar disadvantages.
Other hydrometallurgical processes include the pyrolysis of organic metal salts such as cobalt oxalate, which may also contain bonded water of crystallisation, to produce the metal.
In our European Patent No. 0 0068 853 is described and claimed a process whereby particulate material to be treated is embedded and centrifugally retained within a compact, but turbulent, toroidal bed of further particles within the bed and which circulate about the axis of the processing chamber. Specifically, the resident (xe2x80x9chostxe2x80x9d) particles within the bed are circulated above a plurality of outwardly, radiating, inclined vanes arranged around the base of the processing chamber. Said vanes are preferably arranged in overlapping relationship and the particles are caused to circulate around the bed by the action of a processing fluid, for example gas injected into the processing chamber from beneath and through the vanes.
It has now been found in accordance with the present invention that by selection of a differential terminal velocity between the particles of material within the bed, the rate of circulation of the treated material through the bed may be varied according to the nature of the material to be treated and the desired reaction to be achieved. Surprisingly, complete reaction may be achieved in a matter of milliseconds as compared with the prior art processes which required residence times of a second to several minutes. By xe2x80x9cterminal velocityxe2x80x9d is meant the rate at which a particle, under conditions within the processing chamber, will fall towards the vanes forming the base of the chamber.
Accordingly, in a first aspect the present invention provides a process for treating a particulate material, in which particles of the material to be treated interact with non-static particles of a second material, the process comprising the steps of:
(i) providing a processing chamber having an inlet and an outlet spaced downstream therefrom, the base of said chamber comprising a plurality of outwardly is radiating inclined vanes,
(ii) providing a bed of host particles in the chamber and generating a flow of fluid through the vanes at the base of the processing chamber such that the bed of host particles circulates about an axis of the chamber in a compact turbulent band,
(iii) injecting particles of the material to be treated through an inlet into the chamber to contact with the circulating bed of the host particles,
wherein the relative terminal velocity of the particles to be treated and of the host particles is such that there is little or substantially no migration of the host particles to the outlet, and wherein substantially all of the particles of the material to be treated migrate downstream through the circulating host particles to the outlet.
The flow of fluid may be generated either before or after the host bed of particles is introduced into the chamber. Alternatively, the flow of fluid may be generated as the host bed of particles is introduced into the chamber.
The terminal velocity of the particles will depend upon several parameters, in particular upon density and particle size. In general the average terminal velocity of a host bed particle will be greater than the average terminal velocity of a particle of the material to be treated, prior to the latter being introduced in the chamber. However, the process of the present invention may also be used in circumstances where the terminal velocity of the particles of the material to be treated decreases during processing. In addition, the relative particle size of the material to be treated may be smaller than that of the host particles either initially or resulting from processing through the processing chamber.
Advantageously, the circulating bed of host particles define tortuous paths along which the particles of the material to be treated travel before exiting the processing chamber through the outlet. In an embodiment of the process of the invention the host particles may be withdrawn from the processing chamber from time to time and be replenished with fresh material. Similarly where the host particles are themselves reactive, for example by absorption of released gases from the particles being treated, such host particles may be replenished from time to time.
The particles of the material to be treated preferably enter the chamber below and/or adjacent to the circulating host bed particles in order to contact therewith.
The particles of the material to be treated may be injected into the chamber by conventional means, for example by the use of a compressed fluid, such as compressed air, oxygen, chlorine, ozone, hydrogen, carbon monoxide, sulphur dioxide, hydrogen sulphide, methane, inert gases such as nitrogen, CFC and other noble/-mono-atomic gases.
Heating means are advantageously provided for heating the fluid, such as gas streams produced by the direct combustion of fuels including in-situ combustion of fuels within the bed and indirect heating, for example electrical and microwave. In this case, it will be appreciated that heat transfer may occur between the fluid and the host bed particles and the particles of the material to be treated. Heat transfer will generally also occur between the host bed particles and the particles of the material to be treated.
Separate heating means may also be provided for heating the processing chamber.
An exhaust flow of the fluid may be generated through the outlet of the processing chamber, whereby processed matter is carried in the exhaust flow for withdrawal from the processing chamber to, for example, a cyclone. It will be appreciated that the outlet is vertically spaced above the inlet of the processing chamber.
The host bed of particles typically have an average size of from about 1 to about 6 mm, more typically from about 2 to about 3 mm.
The particles of the material to be treated will generally have an average size of less than about 1000 xcexcm, preferably less than about 600 xcexcm and typically fall in the range of from about 50 to about 600 xcexcm, more typically less than about 300 xcexcm. The process may also be used to treat very fine feedstocks having an average size in the range of from about 1 to about 500 xcexcm, preferably less than about 100 xcexcm, more preferably less than about 50 xcexcm, more preferably less than about 5 xcexcm, still more preferably less than about 1 xcexcm.
The host bed particles may comprise an inert material which does not react with the particles of the material to be treated, such as ceramics, alumina, silica, limestone, and zeolites or, alternatively, may be a material which acts as a catalyst for the reaction of the particles to be treated, such as polyvalent metal salts or activated carbon and in the latter case arrangements must be made to replenish the host bed.
The process of the present invention is particularly suitable for the treatment of sulphide ores, such as, for example, PbS, Cu2S, FeS, NiS and ZnS. In this case, the host bed may comprise particles of a material which is capable of absorbing sulphurous oxides e.g. limestone, quicklime, alumina, sodium based/bearing materials, molecular sieves and silica gel.
The processing chamber may be heated depending on the material to be treated. The host particles may be heated to a temperature in the range of from about 150 to about 1800xc2x0 C., typically from about 150 to about 1400xc2x0 C., more typically from about 300 to about 1200xc2x0 C., still more typically from about 800 to 1200xc2x0 C. Some types of reaction, for example loss of water of crystallisation and solvent removal, may occur at the lower end of the temperature range.
The particles of the material to be treated typically spend on average from about 1 to about 2000 ms in the circulating host bed of particles, preferably from about 5 to about 2000 ms, more preferably from about 5 to about 1000 ms, more preferably from about 5 to about 50 ms, still more preferably from about 10 to about 50 ms.
The flow of fluid through the chamber may be generated in a manner as described in EP-B-0 382 769 and EP-B-0 068 853, i.e. by supplying a flow of fluid into and through the processing chamber and directing the flow by means of the plurality of outwardly is radiating and preferably overlapping vanes arranged in the form of a disc and located in the processing chamber at or adjacent the base thereof. The vanes are inclined relative to the base of the chamber so as to impart rotational motion to the fluid entering the chamber, hence causing the fluid to circulate about a substantially vertical axis of the chamber as it rises.
The particles of the material to be treated will generally enter the chamber below and/or adjacent to the circulating resident bed particles in order to contact therewith. Alternatively, if the inlet is vertically spaced above the vanes at the base of the chamber and the circulating resident bed, then the particles of the material to be treated will fall down through the chamber, under the action of gravity, on to the circulating resident bed. This may be achieved by, for example, a gravity feed mechanism provided in a vertical wall of the chamber.
In a second aspect the present invention provides a reactor suitable for use in the process according to the present invention.
The reactor depends on a stream of fluid which is directed through a chamber containing a set of host particles which are made to circulate about a vertical axis as an annular bed. The host particles are proportioned to remain resident in the chamber as the fluid flows through the chamber. This arrangement permits the reactor to be used in a variety of processes. Firstly, by entraining feed material in particulate form in the stream of fluid, the feed material can be made to pass through the host particles where there is a very fast inter-reaction which may be chemical or thermodynamic, or a combination of both.
In a preferred embodiment of the reactor, the reactor also provides for replacement of the host particles. To do this the reactor includes at least one inlet and one outlet adjacent the set of host material so that fresh host particles may be fed into the bed as spent host particles leave through the outlet sufficient to maintain the function of the bed of host particles.
The reactor makes it possible to use a variety of host particles for different purposes and also to treat the particles themselves. For instance, the feed material may be subjected to a chemical process at an elevated temperature created by using a heated fluid stream. This process could be exothermic or endothermic. The host particles would then be an inert material which is fed through the chamber continuously and treated externally to maintain a steady temperature in the chamber.
In another use of the reactor, the host particles would be chemically active in the process and require replacement. This can be achieved continuously or intermittently as desired.
Still another use would be in the regeneration of catalyst materials. These materials would be in place as host material and exposed to the fluid stream with or without feed material to treat the catalyst material which can be fed through the chamber for regeneration.
Other processes can be conducted in the reactor limited only by the need for the host particles to remain in an annular bed in the chamber.
Accordingly, in the second aspect of the present invention there is provided in a first embodiment a reactor for exposing host particles to a fluid, the reactor having:
an annular chamber disposed about a vertical axis;
an annulus of fluid inlets at the bottom of the chamber and arranged to direct fluid upwardly in a swirling action to generate flow upwardly and about said axis;
a fluid supply coupled to the inlets to provide fluid to the chamber through the inlets;
a fluid outlet at the top of the chamber to divert spent fluid from the chamber;
a second inlet for directing host particles into the chamber to become resident in an annular bed above the fluid inlets so that fluid and host particles will travel about said axis to expose the host particles to the fluid;
a second outlet for directing host particles out of the chamber as they are replaced by host particles entering through the second inlet; and
whereby the reactor receives a supply of host particles sufficient to maintain interaction with the fluid.
In this embodiment the reactor preferably further includes a supply structure in the fluid inlet, the supply structure being arranged to provide feed material in particulate form of a type capable of entrainment in the supply of fluid so that the feed material is carried into the chamber, interacts with the host particles and leaves with the fluid through the fluid outlet.
In a second embodiment, there is provided a reactor for treating feed material in a fluid, the reactor having:
an annular chamber disposed about a vertical axis;
an annulus of fluid inlets at the bottom of the chamber and arranged to direct fluid upwardly in a swirling action to generate flow upwardly and about said axis;
a fluid supply coupled to the inlets to provide fluid to the chamber through the inlets;
a fluid outlet at the top of the chamber to divert spent fluid from the chamber;
a supply structure in the fluid inlet and arranged to provide feed material in particulate form of a type capable of entrainment in the supply of fluid so that the feed material is carried into the chamber to interact with the fluid in an annular bed in the chamber before being carried by the fluid through the outlet.
In the second embodiment the reactor preferably further includes:
a second inlet for directing host particles into the chamber to become resident in an annular bed above the fluid inlets so that feed material and host particles will travel about said axis to expose the host particles to the feed material;
a second outlet for directing host particles out of the chamber; and
whereby the apparatus receives a supply of host particles sufficient to maintain interaction between the host particles and the feed material.